Passive millimeter-wave detector

ABSTRACT

Disclosed are passive millimeter wave detection devices that in some embodiments are useful for detecting objects such as weapons obscured underneath clothing. Also disclosed are methods for detecting objects using millimeter waves, in some embodiments, objects such as weapons, obscured underneath clothing.

RELATED APPLICATION

The present application is the US National Phase entry ofPCT/IB2012/051783 having an International Filing Date of Apr. 12, 2012that was published on Oct. 18, 2012 as WO 2012/140587 and gains priorityfrom U.S. Provisional Patent Application No. 61/475,692 filed Apr. 15,2011, both which are incorporated by reference as if fully set forthherein.

FIELD AND BACKGROUND OF THE INVENTION

The invention, in some embodiments, relates to the field of detectiondevices and more particularly, in some embodiments, to passive detectiondevices and methods using electromagnetic radiation having millimeterwavelengths.

Detection of objects obscured from view is a long standing need invarious fields such as in defense and security, medicine, industry andtransportation. An object may be obscured from view if it is preventedfrom reflecting or emitting light, such as when located in a dark room,or if located behind an opaque or light-scattering medium, such as whenlocated in fog or smoke, or when located on the body of a person andobscured behind clothing.

As is well known in the art of detection devices, an object emitselectromagnetic radiation with an intensity that is dependent on thetemperature and the emissivity of the object. An object at a lowertemperature emits less radiation than the same object at a highertemperature and, at equal temperatures, an object having a higheremissivity emits more radiation than an object having a loweremissivity.

This characteristic of electromagnetic radiation has been used to createimaging devices configured to provide images of objects usingnon-visible electromagnetic radiation (e.g., IR, X-ray), which devicesare often used for detecting concealed objects. However, the use of suchdevices, particularly in contexts such as homeland security, is limitedor prohibited due to physical constraints, safety regulations, privacyviolation limitations, physical size and high cost.

Detection devices operating in the millimeter-wave range ofelectromagnetic radiation, that is radiation having wavelengths in therange of 1 to 10 millimeter which corresponds to frequencies of 30 to300 GHz, overcome some of the problems presented by detection devicesusing electromagnetic radiation having wavelengths in other ranges.

Specifically, millimeter-wave electromagnetic radiation can penetratemany screening materials, such as fog, smoke, carton, sheets of plastic,and clothing. Additionally, millimeter-wave detection allows formillimeter-scale detection resolution. Furthermore, with respect tomillimeter-wave radiation, the attenuation and reflectioncharacteristics of ceramic, metallic, and plastic weapons, as well ascontrabands such as narcotics, are different from the characteristics ofhuman skin, thereby enabling detection of such objects concealed on aperson's body.

Publications related to the use of millimeter-wave radiation in thefield of detection devices include: U.S. Pat. No. 5,073,782; U.S. Pat.No. 5,760,397; U.S. Pat. No. 6,777,684; U.S. Pat. No. 6,950,054; U.S.Pat. No. 6,967,612; US 2005/0099330; US 2009/0195435 as well as thenon-patent publications:

-   Appleby R in “Passive Millimeter-Wave Imaging and How It Differs    From Terahertz Imaging,” Phil Trans R Soc, London, A (2004) 362,    379-394;-   Yujiri L, Shoucri M, Moffa P in “Passive Millimeter Wave Imaging,”    IEEE Microwave Magazine 2003, September, 39-50;-   Manasson V A, Sadovnik L S, Mino R, Rodionov S in “Novel Passive    Millimeter Wave Imaging System: Prototype Fabrication and Testing”    Passive Millimeter-Wave Imaging Technology, Proc. SPIE Optical    Engineering 2000, v. 5070, 21 April, 2-13;-   Kapilevich B, Litvak B, Einat M, Shotman O in “Passive mm-Wave    Sensor for Indoor and Outdoor Homeland Security Applications” Proc.    2007 International Conference on Technologies and Applications,    Spain, 20-23;-   Sheen D M, McMakin D L, Hall T E in “Three-Dimensional    Millimeter-Wave Imaging for Concealed Weapon Detection,” IEEE    Transactions On Microwave Theory and Techniques 2001, v. 49, n. 9,    1581-1592;-   Sheen D M, McMakin D L, Lechelt W M, Griffin J W in “Circularly    Polarized Millimeter-Wave Imaging For Personnel Screening” Proc.    SPIE Optical Engineering 2005, v. 5789, 21, April, 117-126;-   Kapilevich B, Einat M, Litvak B, Shulsinger A, Nehemia E in    “Experimental Study of Indoor mm-Wave Imaging Resolution Limits”    Workshop Nefertiti-2005, Brussels, paper #111;-   Boykin R D in “A Brief Overview of T-ray (THz) Imaging”, DX2 Report,    May 12, 2005,    http://ric.uthscsa.edu/personalpages/lancaste/DI2_Projects_(—)2005/T-Ray.pdf;-   Cooper K B, Dengler R J, Chattopadhyay G, Schlecht E, Gill J,    Skalare A, Mehdi I, Siegel P H in “A High-Resolution Imaging Radar    at 580 GHz”, IEEE microwave and wireless components letters 2008, v.    18, n. 1, January, 64-66;-   Dickinson J C, Goyette T M, Gatesman A J, Joseph C S, Root Z G,    Giles R H, Waldman J, Nixon W E, “Terahertz imaging of subjects with    concealed weapons” Proc. SPIE 2006, vol. 6212, 62120Q01-62120Q12;-   Kemp M C, Taday P F, Cole B E, Cluff J A, Fitzgerald A J, Tribe W R,    “Security Applications of Terahertz Technology,” Proc. SPIE 2003, v.    5070, 44-52;-   Petkie D T, DeLucia F C, Casto C, Helminger P, Jacobs E L, Moyer S    K, Murrill S, Halford C, Griffin S, Franck C in “Active and Passive    Millimeter and Sub-Millimeter-Wave Imaging,” Proc. SPIE 2005, v.    5989, 598918-1-598918-8;-   Tryon G, “Passive Millimeter-Wave Object Detection and People    Screening”, presentation at 2007 SURA Terahertz Applications    Symposium June 6-8, Washington, D.C.; and-   McMillan R W, Currie N C, Ferris D D, Wicks M C Jr. in “Concealed    Weapon Detection Using Microwave and Millimeter Wave Sensors”    Microwave and Millimeter Wave Technology Proc 1998 ICMMT'98, 1-4.

A challenge is how to practically make use of the advantages ofmillimeter-wave radiation in the field of detection devices.

SUMMARY OF THE INVENTION

The invention, in some embodiments, relates to the field of detectiondevices and more particularly, in some embodiments, to passive detectiondevices and methods using electromagnetic radiation having millimeterwavelengths for detection.

According to an aspect of some embodiments of the invention there isprovided a method for detecting a concealed object in a region ofinterest on a person, comprising:

-   -   scanning the region of interest using a passive millimeter-wave        detector comprising an antenna configured to receive millimeter        wave radiation;    -   providing to a processor an output of the scanning by the        detector, which output comprises a signal corresponding to an        intensity of the received millimeter wave radiation;    -   in the processor, storing the output of the scanning;    -   in the processor, processing a plot corresponding to the stored        output to identify whether the plot is unimodal or bimodal; and    -   indicating a result to an operator of the detector, wherein:        -   if the plot is bimodal, indicating to the operator that a            concealed object is potentially detected.

In some embodiments, the indicating the result comprises, if the plot isunimodal, indicating to the operator that no concealed object isdetected.

In some embodiments, the method further comprises calibrating thepassive millimeter-wave detector by scanning an exposed portion of theperson, outside the region of interest, prior to the scanning the regionof interest.

In some embodiments, the passive millimeter-wave detector has dimensionsand weight that allow one-handed operation.

In some embodiments, the passive millimeter-wave detector receives powerfrom a portable power source.

In some embodiments, the antenna has a main lobe having an angular widthin the range of 1 degree to 12 degrees. In some embodiments, the antennahas a main lobe having an angular width in the range of 2 degrees to 9degrees.

In some embodiments, the antenna comprises a horn antenna. In some suchembodiments, the antenna comprises a focusing lens configured to focusincoming millimeter wave radiation into the horn antenna.

In some embodiments, the intensity is of a portion of the receivedmillimeter wave radiation having a frequency between 30 GHz and 300 GHz.In some embodiments, the intensity is of a portion of the receivedmillimeter wave radiation having a frequency between 70 GHz and 110 GHz.In some embodiments, the intensity is of a portion of the receivedmillimeter wave radiation having a frequency between 91 GHz and 97 GHz.

In some embodiments, the indicating that a concealed object ispotentially detected comprises providing a visual indication to theoperator. In some such embodiments, the visual indication is selectedfrom a group consisting of operating a single light, operating multiplelights, continuous operation of a light, periodic operation of a light,and operation of lights in different colors.

In some embodiments, the indicating that a concealed object ispotentially detected comprises providing an aural indication to theoperator (in some embodiments together with a visual indication asdescribed above and in some embodiments without a visual indication asdescribed above). In some such embodiments, the aural indication isselected from a group consisting of a beeping sound, a buzzing sound, acontinuous sound, a periodic sound, a soothing sound, and a bell sound.

In some embodiments, the indicating that a concealed object ispotentially detected comprises providing a tactile indication to theoperator (in some embodiments together with a visual and/or auralindication as described above, in some embodiments without one or bothof visual and/or aural indication as described above). In some suchembodiments, the tactile indication comprises vibration.

In some embodiments, the indicating that no concealed object wasdetected comprises providing a visual indication to the operator. Insome such embodiments, the visual indication is selected from a groupconsisting of operating a single light, operating multiple lights,continuous operation of a light, periodic operation of a light, andoperation of lights in different colors.

In some embodiments, the indicating that no concealed object wasdetected comprises providing an aural indication to the operator (insome embodiments together with a visual indication as described aboveand in some embodiments without a visual indication as described above).In some such embodiments, the aural indication is selected from a groupconsisting of a beeping sound, a buzzing sound, a continuous sound, aperiodic sound, a soothing sound, and a bell sound.

In some embodiments, the indicating that no concealed object wasdetected comprises providing a tactile indication to the operator (insome embodiments together with a visual and/or aural indication asdescribed above, in some embodiments without one or both of visualand/or aural indication as described above). In some such embodiments,the tactile indication comprises vibration.

In some embodiments, the method also comprises providing to the operatoran indication of the intensity of the received millimeter waveradiation. In some such embodiments, the indication is provided at anindicating rate. In some embodiments, the providing the indication ofthe intensity comprises using a plurality of lights, and activating afraction of the plurality of lights in order to provide indication tothe operator, wherein the size of the fraction corresponds to theintensity.

In some embodiments, the method further comprises, during the scanning,projecting a visible light indicating to the operator an area in theregion of interest from which millimeter wave radiation is currentlybeing received by the antenna. In some such embodiments, the projectingcomprises projecting visible light marking the center of the area. Insome such embodiments, the projecting comprises projecting visible lightforming a light cone having an angular width corresponding to an angularwidth of a main lobe of the antenna and illuminating an areasubstantially overlapping the area. In some such embodiments, theprojecting comprises projecting multiple beams of light which impinge onthe region of interest to produce a plurality of light spots delineatingthe borders of the area.

In some embodiments, the processing comprises:

-   -   defining first, second, and third thresholds:        -   the first threshold corresponding to an intensity level            which is above a background intensity level,        -   the second threshold corresponding to an intensity level            which is below an intensity level received from an exposed            area on the person, and        -   the third threshold corresponding to an intensity level            which is a less than the second threshold and greater than            the first threshold and is considered to be above an            intensity level received from an area on the person where a            concealed object is suspected; and    -   identifying a relationship between the plot and the first,        second, and third thresholds, wherein:        -   if during the scanning, the plot rises above the first            threshold and the second threshold, subsequently drops below            the third threshold, subsequently rises above the second            threshold, and subsequently drops below the first threshold,            identifying the plot as bimodal.

In some such embodiments, the identifying the relationship comprises: ifduring the scanning the plot rises above the first threshold and thesecond threshold, and subsequently drops below the second threshold andbelow the first threshold, without dropping below the third threshold,identifying the plot as unimodal. In some such embodiments, the thirdthreshold is set to 80% of the second threshold. In some suchembodiments, the third threshold is set to 90% of the second threshold.In some embodiments, the level of the third threshold may be adjusted bythe operator, based on at least one of the expected concealed object,environmental conditions, and detection resolution.

According to an aspect of some embodiments of the invention there isalso provided a passive millimeter wave detector, comprising:

-   -   a directional antenna configured to receive millimeter wave        radiation having an intensity from a region of interest, and to        output an electrical signal having an amplitude corresponding to        the intensity;    -   a high-frequency amplifier functionally associated with the        directional antenna and configured to receive the electrical        signal, to modulate the electrical signal using a modulating        signal, to amplify components of the electrical signal having        high frequency, and to provide as output an amplified modulated        signal corresponding to the electrical signal having amplified        high frequency components;    -   a high-frequency detector functionally associated with the        high-frequency amplifier and configured to receive the amplified        modulated signal, to restore the modulating signal, and to        provide as output a demodulated electrical signal corresponding        in amplitude to the amplitude of the electrical signal;    -   a low-frequency amplifier functionally associated with the        high-frequency detector and configured to receive the        demodulated electrical signal, to amplify components of the        demodulated electrical signal having low-frequency, and to        provide as output a signal having an amplitude corresponding to        the amplitude of the demodulated electrical signal, in digital        format; and    -   an intensity indicator functionally associated with the        low-frequency amplifier and configured to receive the signal in        the digital format and to indicate the intensity of the received        millimeter wave radiation.

In some embodiments, the detector has dimensions and weight that allowit to be operated as a hand-held device. In some such embodiments, thedetector can be operated using one hand.

In some embodiments, the detector receives power from a portable powersource.

In some embodiments, the antenna has a main lobe having an angular widthin the range of 1 degree to 12 degrees. In some embodiments, the antennahas a main lobe having an angular width in the range of 2 degrees to 9degrees.

In some embodiments, the antenna comprises a horn antenna. In some suchembodiments, the antenna comprises a focusing lens configured to focusincoming millimeter wave radiation into the horn antenna.

In some embodiments, the high-frequency amplifier is configured toamplify components of the electrical signal received from the antennahaving frequencies of 70 GHz and higher. In some embodiments, thehigh-frequency amplifier is configured to amplify components of theelectrical signal received from the antenna having frequencies of 91 GHzand higher.

In some embodiments, the low-frequency amplifier is configured toamplify components of the electrical signal received from the antennahaving frequencies up to 110 GHz. In some embodiments, the low-frequencyamplifier is configured to amplify components of the electrical signalreceived from the antenna having frequencies up to 97 GHz.

In some embodiments, the high-frequency amplifier comprises:

-   -   a pulse generator configured to generate a modulating signal;    -   a PIN switch configured to receive the electrical signal from        the antenna and the modulating signal from the pulse generator,        and to modulate the electrical signal using the modulating        signal to provide a modulated electrical signal;    -   an isolator configured to receive the modulated electrical        signal and to provide band matching of the modulated electrical        signal; and    -   a low noise amplifier (LNA) configured to receive the modulated        electrical signal following the band matching and to amplify the        modulated electrical signal.

In some such embodiments, the modulating signal comprises a 1 KHz signaland the modulated electrical signal comprises a 1 KHz modulatedelectrical signal.

In some embodiments, the low-frequency amplifier comprises:

-   -   a low pass filter configured to filter the received        low-frequency signal to provide a filtered low-frequency signal;    -   a video amplifier configured to amplify the filtered        low-frequency signal to provide an amplified low-frequency        signal; and    -   an active band pass filter configured to filter the amplified        low-frequency signal thereby to improve the noise performance of        the detector.

In some such embodiments, the low pass filter comprises a 30 KHz lowpass filter. In some such embodiments, the active band pass filtercomprises a 1 KHz band pass filter.

In some embodiments, the intensity indicator comprises a plurality oflights, and is configured to indicate the intensity by activating afraction of the plurality of lights, wherein the size of the fractioncorresponds to the intensity.

In some embodiments, the detector also comprises a processor,functionally associated with the low-frequency amplifier and with theintensity indicator, and configured to:

-   -   during a period of time receive and store the output signal of        the low-frequency amplifier in the digital format;    -   identify whether a plot of the stored output signal in the        second format is unimodal or bimodal; and    -   provide an indication to an operator of the detector, wherein:        -   if the plot is bimodal, the indication indicates the            detection of a suspected concealed object.

In some such embodiments, if the plot is unimodal, the indicationindicates the absence of a concealed object.

In some embodiments, the processor is configured to:

-   -   define first, second, and third thresholds:        -   the first threshold corresponding to an intensity level            which is above a background intensity level,        -   the second threshold corresponding to an intensity level            which is below an intensity level received from an exposed            area on the person, and        -   the third threshold corresponding to an intensity level            which is a less than the second threshold and greater than            the first threshold and is considered to be above an            intensity level received from an area on the person where a            concealed object is suspected; and    -   identify a relationship between the plot and the first, second,        and third thresholds, wherein:        -   if during the scanning the plot rises above the first            threshold and the second threshold, subsequently drops below            the third threshold, subsequently rises above the second            threshold, and finally drops below the first threshold,            identify the plot as bimodal.

In some such embodiments, if during the scanning the plot rises abovethe first threshold and the second threshold, and subsequently dropsbelow the second threshold and below the first threshold, withoutdropping below the third threshold, the processor is configured toidentify the plot as unimodal. In some such embodiments, the processoris configured to set the third threshold to 80% of the second threshold.In some such embodiments, the processor is configured to set the thirdthreshold to 90% of the second threshold. In some embodiments, the levelof the third threshold is set by the operator, based on at least one ofthe expected concealed object, environmental conditions, and detectionresolution.

In some embodiments, the processor is configured to provide theindication using the intensity indicator. In some embodiments, theindication comprises a visual indication. In some embodiments, theindication comprises an aural indication. In some embodiments, theindication comprises a tactile indication.

In some embodiments, the detector also comprises at least onedirectional light source configured, during operation of the antenna, toproject visible light indicating an area in the region of interest fromwhich millimeter wave radiation is currently being received by theantenna. In some embodiments, the at least one directional light sourcecomprises a single light source projecting a beam of light generallyparallel to an axis of a main lobe of the antenna and marking a centerof the area. In some embodiments, the at least one directional lightsource comprises a flash light including a reflector projecting lightforming a light cone having an angular width corresponding to an angularwidth of a main lobe of the antenna and illuminating an areasubstantially overlapping the area.

In some embodiments, the at least one directional light source comprisesmultiple light sources projecting multiple beams of light which impingeon the region of interest to produce light spots delineating the bordersof the area. In some such embodiments, the multiple light sources aremounted above a periphery of the antenna. In some such embodiments, themultiple beams of light are divergent from an axis of a main lobe of theantenna. In some such embodiments, the multiple beams of light aredivergent from an axis of a main lobe of the antenna by half the angularwidth of the main lobe of the antenna.

As used herein, the terms “comprising”, “including”, “having” andgrammatical variants thereof are to be taken as specifying the statedfeatures, integers, steps or components but do not preclude the additionof one or more additional features, integers, steps, components orgroups thereof. These terms encompass the terms “consisting of” and“consisting essentially of”.

As used herein, the indefinite articles “a” and “an” mean “at least one”or “one or more” unless the context clearly dictates otherwise.

BRIEF DESCRIPTION OF THE FIGURES

Some embodiments of the invention are described herein with reference tothe accompanying figures. The description, together with the figures,makes apparent to a person having ordinary skill in the art how someembodiments of the invention may be practiced. The figures are for thepurpose of illustrative discussion and no attempt is made to showstructural details of an embodiment in more detail than is necessary fora fundamental understanding of the invention. For the sake of clarity,some objects depicted in the figures are not to scale.

In the Figures:

FIG. 1 is a schematic depiction an embodiment of a detection deviceaccording to the teachings herein;

FIG. 2A is a block diagram depiction of a circuit for operating aprocessor forming part of the detection device of FIG. 1 according tothe teachings herein;

FIG. 2B is a schematic depiction of an embodiment of an electricalcircuit implementing the circuit of FIG. 2A according to the teachingsherein;

FIGS. 3A and 3B are graphical depiction of two plots representingscanned radiation measurements using the detection device of FIG. 1according to the teachings herein; and

FIGS. 4A and 4B are pictorial illustrations of a method of detectingconcealed objects using the detection device of FIG. 1 according to theteachings herein.

DESCRIPTION OF SOME EMBODIMENTS OF THE INVENTION

The invention, in some embodiments thereof, relates to passive methodsand devices for detection of concealed objects, such as weapons,explosives, and contraband materials, using millimeter-wave radiation.

The principles, uses and implementations of the teachings herein may bebetter understood with reference to the accompanying description andfigures. Upon perusal of the description and figures present herein, oneskilled in the art is able to implement the invention without undueeffort or experimentation.

Before explaining at least one embodiment in detail, it is to beunderstood that the invention is not necessarily limited in itsapplication to the details of construction and the arrangement of thecomponents and/or methods set forth herein. The invention is capable ofother embodiments or of being practiced or carried out in various ways.The phraseology and terminology employed herein are for descriptivepurpose and should not be regarded as limiting.

In accordance with the teachings herein, and as will be described infurther detail hereinbelow, a concealed object can be detected byreceiving and analyzing the intensity of millimeter waves emitted from alocation where the concealed object is suspected to be. For example, inaccordance with some embodiments of the teachings herein, millimeterwaves can be used to detect an object of lossy plastic, that is plasticthat is not electrically isolating thereby capable of conductingelectric current, such as typical explosives, or an object of metalcarried by a person and concealed beneath clothing.

Additionally, it is appreciated that the intensity of millimeter wavesemitted by a clothed person under “normal conditions”, e.g., at anairport or along a road, is sufficient to be easily detected at usefuldistances (100 to 400 cm) and differentiated from the background using apassive millimeter-wave detector in accordance with the teachings hereinas described hereinbelow, for example with reference to FIG. 1.

As is further described hereinbelow, Applicant has found that typicalconcealed objects of interest in the field of security, including metalobjects such as knives and guns or plastic explosives, are sufficientlylarge and emit an intensity of millimeter-waves that is sufficientlydifferent from of a living body that such objects are easily detectableusing embodiments of a passive millimeter-wave detector according to theteachings herein, even when concealed beneath clothing.

Thus, according to an aspect of some embodiments of the invention thereis provided a method for detecting a concealed object in a region ofinterest on a person, comprising:

-   -   scanning the region of interest using a passive millimeter-wave        detector comprising an antenna configured to receive millimeter        wave radiation;    -   providing to a processor an output of the scanning by the        detector, which output comprises a signal corresponding to an        intensity of the received millimeter wave radiation;    -   in the processor, storing the output of the scanning;    -   in the processor, processing a plot corresponding to the stored        output to identify whether the plot is unimodal or bimodal; and    -   indicating a result to an operator of the detector, wherein:        -   if the plot is bimodal, indicating to the operator that a            concealed object is potentially detected.

According to an aspect of some embodiments of the invention there isalso provided a passive millimeter wave detector, comprising:

-   -   a directional antenna configured to receive millimeter wave        radiation having an intensity from a region of interest, and to        output an electrical signal having an amplitude corresponding to        the intensity;    -   a high-frequency amplifier functionally associated with the        directional antenna and configured to receive the electrical        signal, to modulate the electrical signal using a modulating        signal, to amplify components of the electrical signal having        high frequency, and to provide as output an amplified modulated        signal corresponding to the electrical signal having amplified        high frequency components;    -   a high-frequency detector functionally associated with the        high-frequency amplifier and configured to receive the amplified        modulated signal, to restore the modulating signal, and to        provide as output a demodulated electrical signal corresponding        in amplitude to the amplitude of the electrical signal;    -   a low-frequency amplifier functionally associated with the        high-frequency detector and configured to receive the        demodulated electrical signal, to amplify components of the        demodulated electrical signal having low-frequency, and to        provide as output a signal having an amplitude corresponding to        the amplitude of the demodulated electrical signal, in digital        format; and    -   an intensity indicator functionally associated with the        low-frequency amplifier and configured to receive the signal in        the digital format and to indicate the intensity of the received        millimeter wave radiation.

Reference is now made to FIG. 1, which is a schematic depiction anembodiment of a detection device according to the teachings herein.

As seen in FIG. 1, a detection device 10 comprises a directional antenna12, a high-frequency amplifier 14, a high-frequency detector 15, alow-frequency amplifier 16, an intensity indicator 18, a portable powersource 20, and a processor 22. Device 10 is portable, having dimensionsand weight allowing device 10 to be held and operated with one hand.

Directional antenna 12 is configured to receive millimeter-waveradiation and to output a high-frequency electric signal having anamplitude corresponding to the intensity of the received radiation.

In some embodiments, directional antenna 12 comprises a horn antenna 32,such as a SGH-10-RP000 Standard Gain pyramidal horn commerciallyavailable from Millitech Inc. of Northampton, Mass., USA.

In some embodiments, the directional antenna of a device as describedherein is configured to receive millimeter wave radiation havingwavelengths in the range of 1 to 10 mm. That said any spectral band ofmillimeter waves useful for detecting concealed objects can be used inimplementing embodiments of the teachings herein.

In some embodiments, the directional antenna is configured to receiveradiation in a broad spectral band, but the device is configured to use(for the detection of concealed objects) millimeter-wave radiation inthe spectral band of 70 GHz-110 GHz, which corresponds to wavelengths inthe range of 2.7 mm-4.4 mm. In some embodiments of the detection devicesdescribed herein, the directional antenna is configured to receiveradiation in a broad spectral band, but the device is configured to use(for the detection of concealed objects) millimeter-wave radiation inthe spectral band of 91 GHz-97 GHz, which corresponds to wavelengths inthe range of 3.1 mm-3.3 mm.

Typically, a specific embodiment of a device is configured toadvantageously detect concealed objects at some specified distance. Forexample, for some typical homeland security embodiments, it is preferredto use a device as described herein to detect concealed objects carriedby a person at a range of between 1.5 meters to about 2.5 meters.Specifically, when trying to detect objects at a distance greater than2.5 meters, any small motion of the hand of the operator, such as normalshaking of the hand, potentially impacts detection ability. On the otherhand, use of the device at distances less than 1.5 meters may cause asecurity threat for the operator of the device, due to the need to let apossibly armed person get within 1.5 meters of the operator.

In some embodiments, it is preferred that during use, directionalantenna 12 receive a signal from a signal-receiving area of between 78cm² (corresponding to a circle having a 10 cm diameter) and 706 cm²(corresponding to a circle having a 30 cm diameter) and in someembodiments an area of between 78 cm² and 314 cm² (corresponding to acircle having a 20 cm diameter). A smaller signal receiving areapotentially gives more “false positive” detection due to a greatersensitivity to operator hand-motion and detection of small objects heldby a person that are not dangerous. A larger signal receiving areapotentially gives more “false negative” detection due to less sensitiveto small concealed objects that are potentially dangerous.

Accordingly, in some embodiments, the angular width of a main lobe ofdirectional antenna 12 is between about 12 degrees, which correspond toa circular signal-receiving area of approximately 30 cm in diameter at arange of 1.5 meters, and about 2.3 degrees, which correspond to acircular signal-receiving area of approximately 10 cm in diameter at arange of 2.5 meters. In some such embodiments, the angular width of themain lobe of antenna 12 is between about 8.6 degrees, which correspondto a circular signal-receiving area of approximately 30 cm in diameterat a range of 2.0 meters, and about 2.9 degrees, which correspond to acircular signal-receiving area of approximately 10 cm in diameter at arange of 2.0 meters.

In some embodiments, directional antenna 12 also includes a focusinglens 34, such as a fluorinated hydrocarbon (Teflon®) lens. In some suchembodiments, lens 34 is positioned at a distance d from horn antenna 32,thereby focusing incoming radiation into horn antenna 32.

In some embodiments, the angular width of the main lobe of an antenna ofa detection device as described herein is fixed. That said, in someembodiments, the angular width of the main lobe of an antenna of adetection device as described herein is user-changeable, for example asin device 10, where the angular width of the main lobe of antenna 12 canbe changed by changing the distance d between horn antenna 32 and lens34. An advantage of a detection device having an antenna with auser-changeable main lobe angular width allows selecting an angularwidth suitable for the range at which the device is used to maintain adesired signal receipt circle, as described below. For example, whensuch a device is used at a long range (e.g., 8-10 meters), the angularwidth of the main lobe of the antenna is changed to be smaller than whenthe device is used at a short range (e.g., 1.5-2 meters). In someembodiments, an antenna includes a main-lobe changing mechanism allowinga user to change the angular width of the main lobe of the antenna. Forexample, in some embodiments, a main-lobe changing mechanism of anantenna 12 includes rails on which a lens such as 34 is moveably mountedrelative to a horn antenna such as 32, and also includes a screwmechanism (rotatable using a manual crank or by activating an associatedelectrical motor). Depending on the direction of rotation of the screwmechanism, the distance d between the horn antenna and the lens isincreased or decreased as desired, changing the angular width of themain lobe of the antenna.

High-frequency amplifier 14 is functionally associated with antenna 12.Specifically, high-frequency amplifier 14 receives, as its input, ahigh-frequency signal corresponding to the radiation received by antenna12, and amplifies high-frequency components of the signal relative tolow-frequency components of the signal.

In some embodiments, high-frequency amplifier 14 comprises a PIN switch36, such as a RSP-10-RWASH SPST PIN switch, commercially available fromMillitech Inc. of Northampton, Mass., USA, and a pulse generator 38. Insome embodiments, amplifier 14 further comprises an isolator 40, such asa FBI-10-RSES0 isolator 40, commercially available from Millitech Inc.of Northampton, Mass., USA, and a low noise amplifier (LNA) 42, such asa QLN-9404028-I32 W-band low-noise amplifier (LNA), commerciallyavailable from QuinStar Technology Inc. of Torrance, Calif., USA.

In some such embodiments, the high-frequency signal received fromantenna 12 is modulated in PIN switch 36 by a 1 KHz signal provided bypulse generator 38. The output of PIN switch 36, which is a modulatedsignal, passes through isolator 40 to LNA 42. LNA 42 amplifies themodulated signal, thereby producing as the output of high-frequencyamplifier 14 an amplified, high-frequency, 1 KHz-modulated signal.

high-frequency detector 15 is functionally associated withhigh-frequency amplifier 14.

In some embodiments, high-frequency detector 15 comprises a highsensitivity high-frequency detector 44, such as a DXW-10-SFAS0 highsensitivity high-frequency detector, commercially available fromMillitech Inc. of Northampton, Mass., USA.

In some embodiments, high-frequency detector 15 receives as input theamplified, high-frequency, 1 KHz modulated signal which is the output ofhigh-frequency amplifier 14. The received signal is detected, such as bydetector 44, to restore the modulating 1 KHz signal, which modulatingsignal has an amplitude corresponding to the intensity of thehigh-frequency signal received by antenna 12. High-frequency detector 15produces as its output a low-frequency signal having an amplitudecorresponding to the amplitude of the high-frequency input signal.

Low-frequency amplifier 16 is functionally associated withhigh-frequency detector 15.

In some embodiments, low-frequency amplifier 16 comprises a low passfilter 46 and a video amplifier 47. In some such embodiments, low passfilter 46 is a 30 KHz low pass filter. A combined low pass filter andvideo amplifier is commercially available from Frequency Devices Inc. ofOttawa, Ill., USA as a D-70 component.

In some embodiments, low-frequency amplifier 16 further comprises anactive band pass filter 48, which is preferably a 1 KHz band passfilter.

In use, low-frequency amplifier 16 receives as its input signal theoutput signal of high-frequency detector 15. The received signal passesthrough low pass filter 46, is amplified in amplifier 47, and is thenfiltered in filter 48, to improve the noise performance of device 10.Low-frequency amplifier 16 amplifies low-frequency components of thesignal relative to high-frequency components of the signal and thusproduces as an output a signal, having an amplitude corresponding to theamplitude of the low-frequency input signal, in a format readable byintensity indicator 18 and by processor 22.

Intensity indicator 18, which may be, for example, a Light EmittingDiode (LED) display, or any other suitable, visual, aural, tactile (orcombination of two or more thereof) indicator, is functionallyassociated with low-frequency amplifier 16.

In some embodiments, intensity indicator 18 receives as its input theoutput signal from low-frequency amplifier 16 and indicates the relativeamplitude of the signal. Due to the relationship between the relativeintensity of the millimeter waves received by antenna 12 and theamplitude of the output signal of low-frequency amplifier 16, intensityindicator 18 is an effective indicator for the relative intensity of theradiation received by antenna 12. In some such embodiments, greatersignal amplitude is indicated by a greater number of activated LEDs.

In some embodiments, intensity indicator 18 is configured to indicatethe absence or presence of a concealed object, as described in furtherdetail hereinbelow.

Processor 22 is a digital processor functionally associated withlow-frequency amplifier 16 and with intensity indicator 18.

In some embodiments, the output of low-frequency amplifier 16, havingamplitude corresponding to the intensity of the high-frequency signalreceived by antenna 12, is input to processor 22 which processes andanalyzes the signal. Specifically, processor 22 continuously receivesthe output signal from low-frequency amplifier 16, for example indigital format, and stores in a memory (not shown) a value correspondingto the relative amplitude of the received signal at a predeterminedrate. In some embodiments, processor 22 stores the received signalscontinuously. In some embodiments, processor 22 stores the receivedsignals periodically. In some embodiments, processor 22 stores thereceived signals intermittently.

In some embodiments, processor 22 analyzes a waveform defined by thestored values as a function of time. If the waveform corresponding tothe monitored intensity has unimodal behavior, i.e., substantiallymonotonously increases, subsequently optionally remains substantiallyconstant, and then substantially monotonously decreases, with nosubstantial drop in intensity, processor 22 optionally indicates theabsence of a concealed object. On the other hand, if the waveformcorresponding to the monitored intensity has bimodal behavior, i.e.,substantially monotonously increases, optionally subsequently remainssubstantially constant, and then substantially monotonously decreasesbut includes a substantial drop in intensity in the constant portion, asschematically depicted in FIG. 3B, processor 22 indicates thepossibility that a concealed object has been detected.

In some embodiments, the output of processor 22 is input to indicator18. In some such embodiments, if a unimodal waveform was detected byprocessor 22, indicator 18 indicates the absence of a concealed object,such as by rapidly blinking on and off a single LED, and if a bimodalwaveform was detected by processor 22, indicator indicates the suspectedpresence of a concealed object, such as by rapidly blinking of all theLEDs of the indicator. That said any suitable type of indication(visual, aural, tactile or combinations thereof) may be used. In someembodiments, a green light indicates absence of a concealed object and ared light indicates the presence of such an object. In some embodiments,continuous illumination from one or more light sources indicates theabsence of a concealed object, and flashing, blinking, periodic, orintermittent illumination indicates the presence of a concealed object.

In some embodiments, indicator 18 includes a speaker (not depicted inFIG. 1) in addition or instead of a light, which provides an auralindication in response to the output of processor 22. For example, upondetection of a unimodal waveform, the speaker may output a single beep,indicating the absence of a concealed object, and upon detection of abimodal waveform, the speaker may output a long buzzing sound,indicating the suspected presence of a concealed object. However, anysuitable aural indication may be used, such as a buzzing sound, abeeping sound, a soothing sound, a continuous sound, a periodic sound,and a bell sound.

In some embodiments, indicator 18 includes a tactile indication provider(not depicted in FIG. 1) in addition or instead of a light and inaddition or instead of a speaker, which provides a tactile indication inresponse to the output of processor 22. In some such embodiments, thetactile indication comprises vibration.

Power for operating device 10 is provided by any suitable power source.That said, the fact that the device is a passive device that uses littlepower allows, in some embodiments, for the practical use of portablepower source 20. In some embodiments, the portable power source 20comprises rechargeable batteries known in the art of portable devices,such as NiMH or lithium ion batteries.

In some embodiments, device 10 further includes at least one directionallight source 50, mounted so as to project visible light indicating atleast an approximate location of the main lobe of the antenna 12.

In some embodiments, directional light source 50 is a single laser,projecting light generally in parallel to the main lobe of antenna 12and marking a spot near the center of the area from which the antenna 12receives radiation at a certain range, e.g., 200 cm.

In some embodiments directional light source 50 is a light source, suchas a flashlight, including a reflector, forming a light cone having anangular width corresponding to that of the main lobe of antenna 12 andilluminating an area substantially overlapping the area from whichantenna 12 receives radiation at a certain range, e.g., 200 cm. In otherwords, the light cone generally overlaps a cone forming the field ofview of antenna 12.

In some embodiments directional light source 50 comprises multiplelasers, for example eight class 1 lasers, mounted about the periphery ofantenna 12 and projecting eight laser beams, each individual beam beingslightly divergent from the axis of main lobe of antenna 12. In somesuch embodiments, each individual laser projects light which isdivergent from the axis of the main lobe of antenna 12 by half theangular width of the main lobe of antenna 12, for example between 3° and6°. In some such embodiments, when directional light source 50 isactivated, the laser beams projected from the lasers produce light spotsdelineating a circle on the target, thereby indicating to an operator ofdevice 10 the area at which the main lobe of antenna 12 is directed andfrom which radiation is received.

Reference is now made to FIG. 2A, which is a block diagram depiction ofa circuit for operating a processor forming part of the detection deviceof FIG. 1 according to the teachings herein, and to FIG. 2B, which is aschematic depiction of an embodiment of an electrical circuitimplementing the circuit of FIG. 2A according to the teachings herein.It is appreciated that the implementations shown in FIGS. 2A and 2B aremerely examples, illustrating one way of implementing a processor, suchas processor 22 of the device of FIG. 1 to enable detection of concealedobjects as described hereinbelow with reference to FIGS. 3A and 3B. Thatsaid any other suitable implementation is considered to be in the scopeof the teachings herein.

Reference is now made to FIGS. 3A and 3B, which are graphical depictionof two plots representing scanned radiation measurements using thedetection device of FIG. 1 according to the teachings herein.

According to an aspect of some embodiments, a method is provided forcomparing amplitude values obtained in various time points to oneanother, thereby allocating an identifiable time-dependent variation ofthe amplitude signal, and more specifically, for concluding, if theamplitude has unimodal behavior with no substantial drop in amplitude,that no concealed object has been detected in the region of interest;and if the modulating amplitude has bimodal behavior including asubstantial drop in amplitude, concluding that the substantial drop inamplitude indicates detection of an concealed object in the region ofinterest.

As seen in FIG. 3A, a graph 200 includes a plot 202 of time-dependentamplitude signals, corresponding to the intensity of received radiation,of a single scan of a main lobe of a directional antenna, such asantenna 12 of device 10 of FIG. 1, over a body of a person. Plot 202 isa unimodal plot, representing a typical result of a measurement duringwhich the “target” clothed person within the region of interest is notcarrying a concealed object.

In FIG. 3B, a graph 210 includes a plot 212 of time-dependent amplitudesignals, corresponding to the intensity of received radiation, of asingle scan of a main lobe of a directional antenna, such as antenna 12of device 10 of FIG. 1, over a body of a person. Plot 212 is a bimodalplot, representing a typical result of a measurement during which the“target” clothed person within the region of interest carries an objectobscured underneath clothing.

As seen, both plots 202 and 212 have a left margin 214 and a rightmargin 216 having relatively low amplitudes, corresponding to lowradiation intensity from the background clutter areas and not related tothe body of the scanned person.

Turning specifically to plot 202 in FIG. 3A, from left to right, plot202 rises from left margin 214 to reach a left peak 218 corresponding tothe radiation intensity received from the body. Further to the right,plot 202 reaches a right peak 220 from which the plot drops back toright margin 216.

The rise in plot 202 between left margin 214 and left peak 218corresponds to an increase in the portion of the field of view of theantenna directed at the target person, until the entire field of view ofthe antenna is directed at the target person and receives radiationtherefrom. In a corresponding manner, the drop in plot 202 between rightpeak 220 and right margin 216 corresponds to a decrease in the portionof the field of view of the antenna directed at the target person.

Center 222 of plot 202 has a plateau, corresponding to a substantiallyconstant intensity of radiation detected from the body of thetarget-person and indicating a substantially unchanging intensity ofradiation detected from successive areas covered in the scan.Subsequently plot 202 forms a substantially unimodal function, that insome embodiments is indicative of absence of a concealed object.

Turning now to plot 212 in FIG. 3B, from left to right, plot 212 risesfrom left margin 214 to reach a left peak 228 corresponding to theradiation intensity received from the body. Further to the right, plot212 reaches a right peak 230 from which the plot drops back to rightmargin 216.

As described hereinabove with reference to plot 202, the rise in plot212 between left margin 214 and left peak 228 corresponds to an increasein the portion of the field of view of the antenna directed at thetarget person, until the entire field of view of the antenna is directedat the target person and receives radiation therefrom. In acorresponding manner, the drop in plot 212 between right peak 230 andright margin 216 corresponds to a decrease in the portion of the fieldof view of the antenna directed at the target person.

As seen, the center of plot 212 between left peak 228 and right peak 230comprises a dip 232, corresponding to a drop in the intensity ofradiation detected from the body of the target-person and indicating thepossible presence of a concealed object having a lower emissivity or alower temperature than that of the body of the target person.Subsequently plot 212 is substantially bimodal, that in some embodimentsis indicative of possible presence of a concealed object. Such aconcealed object may be, for example, a mobile phone, a weapon such as agun or knife, or explosives.

According to an aspect of some embodiments, a method is provided foridentifying a variation of the amplitude signal indicative of thepossible presence of a concealed object. A distinct variation from aplateau of the amplitude signal is identified by a signal decreasefollowed by a signal increase such as dip 232 in plot 212. Conversely, asignal increase followed by a signal decrease (a “bump”) identifies aregion of higher temperature or higher emissivity from the surroundings.In some embodiments such identification of a dip or a “bump” of theamplitude signal is performed by a processor such as processor 22 ofdevice 10.

As seen in FIG. 3B, graph 210 further depicts three thresholds, 240(C3), 242 (C2) and 244 (C1). Threshold 240 (C3) is tuned and set at ahigher level than the background level of margins 214 and 216 which ismeasured for example by receiving radiation from the background.Threshold 244 (C1) is tuned and set at a lower level than the left peak228 and right peak 230 representing radiation intensity from a body of aperson, and which can be measured by receiving radiation from a bodypart which is not obscured (e.g., the head). Threshold 242 (C2) is sethigher than the lowest point in dip 232 and is may be set or adjusted byan operator of the detector depending on the properties of the expectedconcealed object, on environmental conditions, and on the detectionresolution. In some embodiments, threshold 242 is set equal to threshold244.

If a concealed object to be detected is expected to have a lowertemperature or a lower emissivity, threshold 242 is defined at asubstantially lower value (e.g., 80%) than the level of the left andright peaks 228 and 230. Amplitude signals in subsequent “real”measurements are compared with threshold 242. Consequently, anytime-dependent variation of a measured amplitude signal which issubstantially in the center of the plot and has a drop lower thanthreshold 242 is identified as indicating the potential presence of aconcealed object.

If a concealed object to be detected is expected to have a highertemperature or a higher emissivity, a higher threshold 242 is definedabove the level of left and right peaks 228 and 230. Consequently, atime-dependent variation of a measured amplitude signal which issubstantially in center of the respective graph and has a peak higherthan threshold 242 is identified as indicating a concealed object.

In some embodiments, both a higher threshold value and lower thresholdvalue are defined for a single device for a given period of uses. Anoperator can adjust these levels in specific situations. For example, anembodiment of a device such as device 10 of FIG. 1 includes a userinterface functionally associated with a device processor, such asprocessor 22 of FIG. 1. The user interface allows an operator toindicate “reference acquisition mode” and then perform a referencemeasurement as described hereinbelow with reference to FIG. 4A. Thelevel of the plateau of plot 202 or of peaks 228 and 230 of plot 212 isstored as the “normal expected intensity value” considering the expectedconditions of use, such as device condition, background noise, andrang). The operator may then use the user interface to set a “higherthreshold” and a “lower threshold” as percentages of the “normalexpected intensity value”, e.g., “higher threshold” is 110% or 120%while “lower threshold” is 90% or 80% of the “normal expected intensityvalue”.

According to some embodiments, a time-dependent amplitude signal thatrises above threshold 240 and then rises further above threshold 244identifies a person in the region of interest. If the amplitude signalthen decreases below threshold 242, and then rises above threshold 242,it is considered that a concealed object has been detected and anindicator, such as indicator 18 of FIG. 1, indicates the detection of aconcealed object. In contrast, if the amplitude signal does not riseabove threshold 242 after a decrease below threshold 242, the indicatordoes not indicate the detection of a concealed object. When theamplitude signal decreases to below threshold 240, it is considered theend of a single scan over the body of the person. If, during the singlescan, the signal did not include a drop requiring the processor toindicate the presence of a concealed object, at the end of the scan theindicator indicates the absence of a concealed object, as describedhereinabove with reference to FIG. 1.

Reference is now made to FIGS. 4A and 4B, which are pictorialillustrations of a method of detecting concealed objects using adetection device according to the teachings herein.

As seen in FIG. 4A, an operator of a detection device 300, similar todevice 10 of FIG. 1, points an antenna 302, similar to antenna 12 ofdevice 10, towards a person. Specifically, in order to obtain areference measurement of the millimeter-wave radiation emitted by theperson, the operator points antenna 302 at a portion of the person whichis not obscured, such as the target person's head.

In some embodiments, the operator identifies the location at which theantenna 302 is directed by using the light 304 formed on the body of theperson from a directional light source such as directional light source50 of FIG. 1.

In some embodiments, the person is located at a distance ofapproximately 2-3 meters from the operator of device 300 when thereference measurement is taken. However, any suitable distance D may beused when carrying out the method described herein.

Turning to FIG. 4B, it is seen that after the reference value isobtained as described with reference to FIG. 4A, the operator scans aregion of interest, such as the body of the person, using the main lobeof antenna 302 of device 300. In some embodiments, the operatoridentifies the location at which antenna 302 is directed by using light304 formed on the body of the person from a directional light sourcesuch as directional light source 50 of FIG. 1.

In some embodiments, the main lobe of antenna 302 is aimed slightly awayfrom the person and device 300 is swung in a direction, for example,from left to right, as indicated by dashed line 308. When the main lobeof antenna 302 is aimed away from the person prior to beginning thescan, for example on the left side of line 308, a background signal isdetected, corresponding to portion 214 of plots 202 and 212 of FIGS. 3Aand 3B.

As the main lobe of antenna 302 covers more of the body of the person,more millimeter wave energy emitted by the person's body is detected sothat the intensity of millimeter waves detected by device 300 increases.Since clothing is transparent to millimeter waves, the intensity of thesignal substantially monotonously increases until the entire main lobeof antenna 302 is aimed at the person.

The intensity of the signal remains substantially constant as long asthe entire main lobe is aimed at the person. When the main lobe reachesthe edge of the person, for example on the right side of the person'sbody, the intensity of the signal decreases substantially monotonouslysince at each moment in time a smaller portion of the field of view ofantenna 302 is directed at the person.

If during the scanning, a portion of the body of the person isobstructed by a sufficiently large object so that a sufficiently largefraction of millimeter waves emitted by the person's body are blocked,such as a mobile phone, knife, pack with explosives or gun obscuredbeneath the clothing, here illustrated as a concealed gun 310 asubstantial drop in the signal intensity is identified by a processor ofdevice 300, similar to processor 22 of FIG. 1. Such a drop is indicativeof the presence of a concealed object, and results in activation of anindicator, such as indicator 18 of FIG. 1, indicating to the operatorthat concealed gun 310 is detected. In the illustrated embodiment, analarm light 320 flashes when a drop in the signal intensity is detected.

In some embodiments, a detection device as described herein includes anarray of directional antennas, the individual antennas aimed atdifferent areas in the region of interest, so that each antenna receivesradiation from a different area. In accordance with some suchembodiments, the detection device having an array of directional antennais useful e.g., for significantly reducing the time required to scan alarge region of interest. By performing a scan in a perpendiculardirection to the direction of a linear array of antennas (e.g., avertical array of antennas and a scan performed in the horizontaldirection), a large region of interest may be covered by a single scan.

It is appreciated that certain features of the invention, which are, forclarity, described in the context of separate embodiments, may also beprovided in combination in a single embodiment. Conversely, variousfeatures of the invention, which are, for brevity, described in thecontext of a single embodiment, may also be provided separately or inany suitable subcombination or as suitable in any other describedembodiment of the invention. Certain features described in the contextof various embodiments are not to be considered essential features ofthose embodiments, unless the embodiment is inoperative without thoseelements.

Although the invention has been described in conjunction with specificembodiments thereof, it is evident that many alternatives, modificationsand variations will be apparent to those skilled in the art.Accordingly, it is intended to embrace all such alternatives,modifications and variations that fall within the scope of the appendedclaims.

The invention claimed is:
 1. A method for detecting a concealed objectin a region of interest on a person, comprising: scanning said region ofinterest using a passive millimeter-wave detector comprising an antennaconfigured to receive millimeter wave radiation; providing to aprocessor an output of said scanning by said detector, which outputcomprises a signal corresponding to an intensity of said receivedmillimeter wave radiation; in said processor, storing said output ofsaid scanning; in said processor, processing a plot corresponding tosaid stored output to identify whether said plot is unimodal or bimodal;and indicating a result to an operator of said detector, wherein: ifsaid plot is bimodal, indicating to said operator that a concealedobject is potentially detected.
 2. A method according to claim 1,wherein said indicating said result comprises, if said plot is unimodal,indicating to said operator that no concealed object was detected.
 3. Amethod according to claim 1, comprising calibrating said detector byscanning an exposed portion of said person, outside said region ofinterest, prior to said scanning said region of interest.
 4. A methodaccording to claim 1, wherein said detector has dimensions and weightthat allow one-handed operation.
 5. A method according to claim 1,wherein said antenna has a main lobe having an angular width in therange of 1 degree to 12 degrees.
 6. A method according to claim 1,wherein said antenna has a main lobe having an angular width in therange of 2 degrees to 9 degrees.
 7. A method according to claim 1,wherein said antenna comprises a horn antenna.
 8. A method according toclaim 7, wherein said antenna comprises a focusing lens configured tofocus incoming millimeter wave radiation into said horn antenna.
 9. Amethod according to claim 1, wherein said intensity is of a portion ofsaid received millimeter wave radiation having a frequency between 30GHz and 300 GHz.
 10. A method according to claim 1, also comprisingproviding to said operator an indication of said intensity of saidreceived millimeter wave radiation.
 11. A passive millimeter wavedetector, comprising: a directional antenna configured to receivemillimeter wave radiation having an intensity from a region of interest,and to output an electrical signal having an amplitude corresponding tosaid intensity; a high-frequency amplifier functionally associated withsaid directional antenna and configured to receive said electricalsignal, to modulate said signal using a modulating signal, to amplifycomponents of said electrical signal having high frequency, and toprovide as output an amplified modulated signal corresponding to saidelectrical signal having amplified high frequency components; ahigh-frequency detector functionally associated with said high-frequencyamplifier and configured to receive said amplified modulated signal, torestore said modulating signal, and to provide as output a demodulatedsignal corresponding in amplitude to said amplitude of said electricalsignal; a low-frequency amplifier functionally associated with saidhigh-frequency detector and configured to receive said demodulatedsignal, to amplify components of said demodulated signal havinglow-frequency, and to provide as output a signal having an amplitudecorresponding to said amplitude of said demodulated signal, in digitalformat; and an intensity indicator functionally associated with saidlow-frequency amplifier and configured to receive said signal in saiddigital format and to indicate said intensity of said receivedmillimeter wave radiation.
 12. A passive millimeter wave detectoraccording to claim 11, wherein said detector has dimensions and weightthat allow it to be operated with one hand.
 13. A passive millimeterwave detector according to claim 11, wherein said antenna comprises ahorn antenna.
 14. A passive millimeter wave detector according to claim13, wherein said antenna comprises a focusing lens configured to focusincoming millimeter wave radiation into said horn antenna.
 15. A passivemillimeter wave detector according to claim 11, wherein saidhigh-frequency amplifier is configured to amplify components of saidelectrical signal received from said antenna having frequencies of 70GHz and higher.
 16. A passive millimeter wave detector according toclaim 11, wherein said low-frequency amplifier is configured to amplifycomponents of said electrical signal received from said antenna havingfrequencies up to 110 GHz.
 17. A passive millimeter wave detectoraccording to claim 11, and further comprising a processor, functionallyassociated with said low-frequency amplifier and with said intensityindicator, and configured to: during a period of time receive and storesaid output signal of said low-frequency amplifier in said digitalformat; identify whether a plot of said stored output signal in saidsecond format is unimodal or bimodal; and provide an indication to anoperator of said detector, wherein: if said plot is bimodal, saidindication indicates the detection of a suspected concealed object. 18.A passive millimeter wave detector according to claim 17, wherein ifsaid plot is unimodal, said indication indicates the absence of aconcealed object.
 19. A passive millimeter wave detector according toclaim 17, wherein said processor is configured to: define first, second,and third thresholds: said first threshold corresponding to an intensitylevel which is above a background intensity level, said second thresholdcorresponding to an intensity level which is below an intensity levelreceived from an exposed area on said person, and said third thresholdcorresponding to an intensity level which is a less than said secondthreshold and greater than said first threshold and is considered to beabove an intensity level received from an area on said person where asaid concealed object is suspected; and identify a relationship betweensaid plot and said first, second, and third thresholds, wherein: ifduring said scanning said plot rises above said first threshold and saidsecond threshold, subsequently drops below said third threshold,subsequently rises above said second threshold, and finally drops belowsaid first threshold, identify said plot as bimodal.
 20. A passivemillimeter wave detector according to claim 11, and also comprising atleast one directional light source configured, during operation of saidantenna, to project visible light indicating an area in said region ofinterest from which millimeter wave radiation is currently beingreceived by said antenna.